How an Earth Orbiting Tether Makes Possible an Affordable Earth-Moon Space Transportation System 942120
The Earth orbiting tether, is based in part on the elevator into space idea that was described by Arthur C. Clark in his book, The Fountains of Paradise. That particular space transportation concept consisted of hanging a cable from geostationary orbit down to the surface of the Earth and moving people and freight from the Earth into space on an elevator which would ascend and descend along the cable.
The tether concept used in this transportation system is an intermediate version of that idea which can be built with existing materials. It works by starting from a much lower altitude orbit and hanging the tether down to just above the Earth's atmosphere. The length of the lower half of the tether is selected such that a suborbital shuttle, built using existing technology, can fly to the lower end of the tether without the need for any additional stages or drop-off external propellant tanks. The length of the upper half of the cable is chosen so that its endpoint is traveling at slightly less than escape velocity for its altitude. This is done so that an Earth-Moon transfer vehicle, upon being released from the upper end of the tether, can be placed in a lunar bound orbit with only minimal use of its onboard propellant.
The transportation system consists of 4 major components:
a reusable single-stage suborbital shuttle that carries people and cargo to the lower end of the tether.
a vertically-oriented, Earth-orbiting tether with a lower endpoint terminal for receiving cargo from the suborbital shuttle, and an upper endpoint terminal for launching and receiving the Earth-Moon Transfer Vehicles.
an Earth-Moon Transfer Vehicle that carries people and cargo back and forth between the tether and lunar orbit.
and a reusable, single-stage Lunar Lander that transfers people and cargo between the lunar surface and lunar orbit.